1. Field of the Invention
The present invention relates to a solvent delivery pump for sucking and discharging a mobile phase by reciprocating a plunger on a straight line and a liquid chromatograph using the solvent delivery pump.
2. Description of the Related Art
In a solvent delivery pump used for sending a mobile phase in a liquid chromatograph, if the solution sending pressure becomes high over 50 MPa, frictional force between a plunger seal sealing a pump chamber and a plunger becomes large. This shortens the life of the plunger seal. Therefore, in order to reduce the frictional force between the plunger seal and the plunger, a mechanism for supplying a cleaning solution to portions of the plunger seal and the plunger sliding on each other to wet an outer peripheral face of the plunger is proposed (see Japanese Patent Application Laid-Open No. 10-238475).
FIG. 3 shows an example of a solvent delivery pump having such a function. At the tip end of a pump body 2, a pump head 8 having, in itself, a pump chamber 8a, a sucking flow path 8b, and a discharge flow path 8c is provided. A cross head 4 is housed in the pump body 2 and biased in a direction opposite from the pump head 8 by a spring 6. A plunger 3 is retained on the tip end of the cross head 4 and the tip end of the plunger 3 is inserted into the pump chamber 8a. 
The cross head 4 is reciprocated on a straight line (in a left-right direction in the drawing) by a driving mechanism (not shown) including a cam and the like, and the plunger 3 also reciprocates on a straight line as the cross head 4 reciprocates to thereby increase and decrease a capacity in the pump chamber 8a. The sucking flow path 8b is connected, via a check valve 10a, to a pipe 29 connected to a vessel for storing the mobile phase. The discharge flow path 8c is connected, via a check valve 10b, for example, to a pipe 28 forming an analytical flow path of the liquid chromatograph.
Between the tip end portion of the pump body 2 and the pump head 8, a plunger seal 12, a seal holder 14, and a cleaning seal 16 are sandwiched in this order from a side of the pump head 8. The plunger seal 12 is for sealing the pump chamber 8a while slidably retaining the plunger 3 at a portion of the pump chamber 8a, into which the plunger 3 is inserted, and the plunger seal 12 is supported on the seal holder 14.
The seal holder 14 includes, in itself, a cleaning chamber 18a and cleaning chamber flow paths 20a and 24a. A pipe 21 assembled to take in a cleaning solution from a vessel storing the cleaning solution with a pump (not shown) to supply it to the cleaning chamber 18a is connected to the cleaning chamber flow path 20a, and a pipe 25 assembled to return the cleaning solution from the cleaning chamber 18a to a vessel for the cleaning solution is connected to the cleaning chamber flow path 24a. The cleaning chamber 18a is sealed with the cleaning seal 16.
By providing a circulating mechanism of the cleaning solution as described above, the cleaning solution is supplied to the cleaning chamber 18a to wet an outer peripheral face of the plunger 3 on a back face side of the plunger seal 12 to reduce friction and increase a sliding property between the plunger 3 and the plunger seal 12. By constantly wetting the back face side of the plunger seal 12, an effect of preventing deposition of salt caused by drying of the back face side of the plunger seal 12 can be obtained.
The above-described solvent delivery pump is provided with vessels for storing the cleaning solution and the pump for circulating the cleaning solution. If these vessels and pump can be omitted, it is possible to reduce the size of a device to reduce an installation space for the device. Moreover, if the pipes for circulating the cleaning solution can be omitted, connection of the pipes is simplified and it becomes easier to detach or assemble the pipes in maintenance. Conventionally, however, it is difficult to reduce the frictional force between the plunger and the plunger seal without such a mechanism.